Known in the art is an internal combustion engine arranging in an engine exhaust passage an NOx storage catalyst storing NOx contained in exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and releasing the stored NOx when the air-fuel ratio of the inflowing exhaust gas becomes a stoichiometric air-fuel ratio or rich. In this internal combustion engine, the NOx produced at the time of combustion under a lean air-fuel ratio is stored in the NOx storage catalyst to thereby prevent the NOx from being exhausted into the atmosphere.
However, the NOx storage ability of this NOx storage catalyst falls the lower the temperature of the NOx storage catalyst. Therefore, when the temperature of the NOx storage catalyst is low, the NOx ends up being exhausted into the atmosphere. Accordingly, there is known an internal combustion engine arranging in an engine exhaust passage upstream of the NOx storage catalyst an NOx adsorption catalyst adsorbing the NOx contained in the exhaust gas at the time of a low temperature and desorbing the adsorbed NOx when the temperature rises (for example, see Patent Literature 1).
In this internal combustion engine, when the temperature of the NOx adsorption catalyst is low such as for example at the time of engine startup, the NOx exhausted from the engine is adsorbed at the NOx adsorption catalyst. When the temperature of NOx adsorption catalyst rises, the NOx is desorbed from the NOx adsorption catalyst and the desorbed NOx is stored in the NOx storage catalyst.